Te Deum

From Conservapedia

The Te Deum was originally a chant of praise or thanksgiving sung during processions or at the end of Matins on Sundays and feast days. Polyphonic settings only appeared in the 16th century, however its use during festivals became popular during the Baroque period and continue to this day. The Haydn brothers, Berlioz, Dvorak and Verdi have written notable settings. Organ settings of Martin Luther's version of the original Gregorian chant were written by various baroque composers including J.S. Bach.